Zinc finger nucleases (fusions of zinc finger domains and cleavage domains) for targeted cleavage of genomic DNA have been described. Such targeted cleavage events can be used, for example, to induce targeted mutagenesis, induce targeted deletions of cellular DNA sequences, and facilitate targeted recombination at a predetermined chromosomal locus. See, for example, United States Patent Publications 20030232410; 20050208489; 20050026157; 20050064474; 20060188987; 20060063231; and International Publication WO 07/014,275, the disclosures of which are incorporated by reference in their entireties for all purposes.
To increase specificity, a pair of fusion proteins, each comprising a zinc finger binding domain and cleavage half-domain can be used to cleave the target genomic DNA. Because cleavage does not occur unless the cleavage half-domains associate to form a functional dimer, this arrangement increases specificity.
However, to further decrease off-target cleavage events, there remains a need for engineered cleavage half-domains that cleave DNA only upon formation of a heterodimer.